A 16-foot sculpture of a female polar bear and her cub floated down the Thames today in a bid to raise awareness of their endangered habitat.The work was commissioned by Eden, a new digital television channel devoted to natural history programming.The sculpture was made by 15 artists over two months, measures 20 foot by 20 foot, weighs 1.5 tonnes and travelled 7.5 miles down the river this morning from Greenwich to the Houses of Parliament.Wildlife broadcaster Sir David Attenborough said: "The melting of the polar bears' sea ice habitat is one of the most pressing environmental concerns of our time. We need to do what we can to protect the world's largest land carnivores from extinction"